Re: [PATCH v2] hw/arm/virt: Expose empty NUMA nodes through ACPI

[Igor Mammedov <imammedo@redhat.com>]

On Fri, 5 Nov 2021 23:47:37 +1100
Gavin Shan <gshan@redhat.com> wrote:

> Hi Drew and Igor,
> 
> On 11/2/21 6:39 PM, Andrew Jones wrote:
> > On Tue, Nov 02, 2021 at 10:44:08AM +1100, Gavin Shan wrote:  
> >>
> >> Yeah, I agree. I don't have strong sense to expose these empty nodes
> >> for now. Please ignore the patch.
> >>  
> > 
> > So were describing empty numa nodes on the command line ever a reasonable
> > thing to do? What happens on x86 machine types when describing empty numa
> > nodes? I'm starting to think that the solution all along was just to
> > error out when a numa node has memory size = 0...

memory less nodes are fine as long as there is another type of device
that describes  a node (apic/gic/...).
But there is no way in spec to describe completely empty nodes,
and I dislike adding out of spec entries just to fake an empty node.


> Sorry for the delay as I spent a few days looking into linux virtio-mem
> driver. I'm afraid we still need this patch for ARM64. I don't think x86

does it behave the same way is using pc-dimm hotplug instead of virtio-mem?

CCing David
as it might be virtio-mem issue.

PS:
maybe for virtio-mem-pci, we need to add GENERIC_AFFINITY entry into SRAT
and describe it as PCI device (we don't do that yet if I'm no mistaken).

> has this issue even though I didn't experiment on X86. For example, I
> have the following command lines. The hot added memory is put into node#0
> instead of node#2, which is wrong.
> 
> There are several bitmaps tracking the node states in Linux kernel. One of
> them is @possible_map, which tracks the nodes available, but don't have to
> be online. @passible_map is sorted out from the following ACPI table.
> 
>    ACPI_SRAT_TYPE_MEMORY_AFFINITY
>    ACPI_SRAT_TYPE_GENERIC_AFFINITY
>    ACPI_SIG_SLIT                          # if it exists when optional distance map
>                                           # is provided on QEMU side.
> 
> Note: Drew might ask why we have node#2 in "/sys/devices/system/node" again.
> hw/arm/virt-acpi-build.c::build_srat() creates additional node in ACPI SRAT
> table and the node's PXM is 3 ((ms->numa_state->num_nodes - 1)) in this case,
> but linux kernel assigns node#2 to it.
> 
>    /home/gavin/sandbox/qemu.main/build/qemu-system-aarch64 \
>    -accel kvm -machine virt,gic-version=host               \
>    -cpu host -smp 4,sockets=2,cores=2,threads=1            \
>    -m 1024M,slots=16,maxmem=64G                            \
>    -object memory-backend-ram,id=mem0,size=512M            \
>    -object memory-backend-ram,id=mem1,size=512M            \
>    -numa node,nodeid=0,cpus=0-1,memdev=mem0                \
>    -numa node,nodeid=1,cpus=2-3,memdev=mem1                \
>    -numa node,nodeid=2 -numa node,nodeid=3                 \
>    -object memory-backend-ram,id=vmem0,size=512M           \
>    -device virtio-mem-pci,id=vm0,memdev=vmem0,node=2,requested-size=0 \
>    -object memory-backend-ram,id=vmem1,size=512M           \
>    -device virtio-mem-pci,id=vm1,memdev=vmem1,node=3,requested-size=0
>       :
>    # ls  /sys/devices/system/node | grep node
>    node0
>    node1
>    node2
>    # cat /proc/meminfo | grep MemTotal\:
>    MemTotal:        1003104 kB
>    # cat /sys/devices/system/node/node0/meminfo | grep MemTotal\:
>    Node 0 MemTotal: 524288 kB
> 
>    (qemu) qom-set vm0 requested-size 512M
>    # cat /proc/meminfo | grep MemTotal\:
>    MemTotal:        1527392 kB
>    # cat /sys/devices/system/node/node0/meminfo | grep MemTotal\:
>    Node 0 MemTotal: 1013652 kB
> 
> Try above test after the patch is applied. The hot added memory is
> put into node#2 correctly as the user expected.
> 
>    # ls  /sys/devices/system/node | grep node
>    node0
>    node1
>    node2
>    node3
>    # cat /proc/meminfo | grep MemTotal\:
>    MemTotal:        1003100 kB
>    # cat /sys/devices/system/node/node2/meminfo | grep MemTotal\:
>    Node 2 MemTotal: 0 kB
> 
>    (qemu) qom-set vm0 requested-size 512M
>    # cat /proc/meminfo | grep MemTotal\:
>    MemTotal:        1527388 kB
>    # cat /sys/devices/system/node/node2/meminfo | grep MemTotal\:
>    Node 2 MemTotal: 524288 kB
> 
> Thanks,
> Gavin
> 
> 
>    
>